This invention is directed to a edge tracking system for use with papermaking machines for maintaining the papermaking fabric aligned during its circulating motion through the papermaking machine and for recording the position of the papermaking fabric during operation of the machine. The tracking system is particularly intended for use in a paper forming section of a papermaking machine, although it is in no way limited to this section, and could well find utility with press machines or drying machines.
In papermaking, continuous porous fabrics are circulated through the papermaking machines along a single vertical plane, but through a plurality of horizontal planes. One of these horizontal planes is designated the forming area and it is in this area that the paper forming pulp of dilute fiber is deposited onto the papermaking fabric. The dilute fiber suspension, consisting of water and 0.2 to 1.0% solids, is discharged at speeds up to 6000 ft/min. on to the moving forming fabric which is moving at a fiber discharge speed of .+-.30 feet/minute. The water is removed by suction through the porous papermaking fabric to form a paper sheet on the surface thereof. The water removal, which results in fiber reorientation, continues until the consistency of the paper forming pulp reaches 20-25% solids.
Due to these high speeds, it has become increasingly important that the papermaking fabrics be maintained aligned as it circulates through the papermaking machine.
In the past, alignment has been carried out mainly by hand using the tensioning apparatus of the papermaking machine. Such a device is disclosed in U.S. Pat. No. 2,918,970 ('970).
There have been attempts to utilize such type devices along with an edge contracting paddle. In this arrangement a pivoted paddle is positioned to engage the moving edge of the papermaking fabric. Transverse movement of the edge moves the paddle about a pivot which actuates an electromechanical device. The electromechanical device then initiates movement of a bearing assembly carrying one end of a papermaking fabric supporting roll. This arrangement lacks the facility of making instantaneous responses and the ability for making minute adjustments is limited. Also, the paddle presents the problem of edge wear which could cause unraveling and thereby shorten the life of the papermaking fabric. Finally, there is a tendency for the pivot arm to stick and fail to react to edge movements.
Accordingly, it is an object of the instant invention to provide an edge tracking system which provides instantaneous response to misalignment of the papermaking fabric.
Another object of the invention is to provide an edge tracking system which is sensitive to minute misalignments of the papermaking fabric.
Another object of the invention is the provision of an edge tracking system which monitors the position of the papermaking fabric, but does not physically contact the fabric.
Another object of the invention is to provide a tracking system including a recording mechanism which operates to plot the position of the papermaking fabric during operation of the papermaking machine.
Another object of the invention is to provide an edge tracking system having an edge sensor which operates without mechanical movement and is effective to detect minute movement.
Another object of the invention is to provide a laser scanner producing a laser curtain having parallel edges for use with a papermaking machine.